U.S. patent number 7,840,719 [Application Number 12/392,246] was granted by the patent office on 2010-11-23 for system and program products for facilitating input/output processing by using transport control words to reduce input/output communications.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Daniel F. Casper, John R. Flanagan.
United States Patent |
7,840,719 |
Casper , et al. |
November 23, 2010 |
System and program products for facilitating input/output
processing by using transport control words to reduce input/output
communications
Abstract
Input/output processing is facilitated by reducing
communications between input/output communications adapters and
control units during input/output processing. The number of
exchanges and sequences between an input/output communications
adapter and control unit is reduced by sending a plurality of
commands from the adapter to the control unit as a single entity
for execution by the control unit. The control unit executes the
commands and provides the data, if any, in one sequence. The
control unit relieves the adapter of the responsibility of tracking
state of the individual commands and is able to calculate precise
measurement data relating to execution of the commands.
Inventors: |
Casper; Daniel F.
(Poughkeepsie, NY), Flanagan; John R. (Poughkeepsie,
NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
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Family
ID: |
39297369 |
Appl.
No.: |
12/392,246 |
Filed: |
February 25, 2009 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090172203 A1 |
Jul 2, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11548060 |
Oct 10, 2006 |
7500023 |
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Current U.S.
Class: |
710/5;
710/35 |
Current CPC
Class: |
G06F
13/126 (20130101) |
Current International
Class: |
G06F
3/00 (20060101); G06F 13/00 (20060101) |
Field of
Search: |
;710/5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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3931514 |
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Mar 1990 |
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DE |
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1264096 |
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Feb 1972 |
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GB |
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2291990 |
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Feb 1996 |
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GB |
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63236152 |
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Oct 1988 |
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JP |
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WO2006102664 |
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Sep 2006 |
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WO |
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Primary Examiner: Tsai; Henry W
Assistant Examiner: Roche; John B
Attorney, Agent or Firm: Cantor Colburn LLP Campbell;
John
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of co-pending U.S. patent
application Ser. No. 11/548,060, filed Oct. 10, 2006, entitled
"FACILITATING INPUT/OUTPUT PROCESSING BY USING TRANSPORT CONTROL
WORDS TO REDUCE INPUT/OUTPUT COMMUNICATIONS," by Casper et al.,
which is hereby incorporated herein by reference in its
entirety
This application also contains subject matter which is related to
the subject matter of the following application, assigned to the
same assignee as this application and hereby incorporated herein by
reference in its entirety:
"FACILITATING ACCESS TO STATUS AND MEASUREMENT DATA ASSOCIATED WITH
INPUT/OUTPUT PROCESSING," Casper et al., (POU920060228US1), U.S.
Ser. No. 11/548,093, filed Oct. 10, 2006, and published on Jun. 19,
2008 as U.S. Publication No. 2008/0147890 A1.
Claims
What is claimed is:
1. A computer program product for facilitating input/output
processing of a processing environment, the computer program
product comprising: a non-transitory storage medium readable by a
processor and storing instructions for execution by the processor
for performing a method comprising: obtaining by an input/output
communications adapter of the processing environment a transport
control word, said transport control word including a count of the
total amount of data being transferred, an address of a descriptor
control block to be sent to a control unit of the processing
environment, in which the descriptor control block includes a
plurality of input/output commands to be executed, an address of a
list that informs the input/output communications adapter where to
store or fetch data received from or transmitted to the control
unit, and an address where to store ending status from the control
unit; forwarding from the input/output communications adapter to
the control unit the descriptor control block that includes the
plurality of input/output commands as one entity, wherein the
forwarding includes forwarding from the input/output communications
adapter to the control unit the descriptor control block including
the plurality of input/output commands in a single communication;
and executing by the control unit the plurality of input/output
commands to perform one or more input/output operations, wherein
the executing is performed absent a tracking by the input/output
communications adapter of state relative to the individual
input/output commands of the plurality of input/output commands
being executed by the control unit.
2. The computer program product of claim 1, wherein the descriptor
control block further comprises a header providing information
relating to the input/output commands to be executed and descriptor
data for one or more of the input/output commands.
3. The computer program product of claim 2, wherein the descriptor
data comprises control data to be provided to a device coupled to
the control unit, the device designated by a device address
specified in the header of the descriptor control block, said
control data being provided to the device absent a separate data
transfer.
4. The computer program product of claim 1, further comprising
applying a checking code to the descriptor control block to enable
the control unit to check validity of the descriptor control
block.
5. The computer program product of claim 1, wherein the list
comprises one or more modified indirect data address words.
6. The computer program product of claim 5, wherein the list of one
or more modified indirect data address words comprises a single
modified indirect data address word list that describes a plurality
of data areas for a plurality of descriptor command words.
7. The computer program product of claim 1, wherein a transfer of
data resulting from the execution of the plurality of input/output
commands is performed using a single exchange between the
input/output communications adapter and the control unit.
8. The computer program product of claim 7, further comprising
applying a checking code to the data being transferred to check
validity of the transferred data.
9. The computer program product of claim 1, further comprising
providing by the control unit to the input/output communications
adapter at least one of data and status resulting from execution of
the plurality of input/output commands, wherein a transfer of data
resulting from the execution of the plurality of input/output
commands is performed using three communication sequences between
the input/output communications adapter and control unit.
10. The computer program product of claim 9, wherein the number of
sequences remains the same, even if the number of input/output
commands indicated by the location specified in the transport
control word increases.
11. The computer program product of claim 1, wherein the
input/output communications adapter comprises a channel, and the
plurality of input/output commands comprise a plurality of channel
commands specified by one or more channel command words, wherein
each channel command word comprises a command code, one or more
flags and a count field.
12. A system of facilitating input/output processing of a
processing environment, the system comprising: an input/output
communications adapter of the processing environment to obtain a
transport control word, said transport control word including a
count of the total amount of data being transferred, an address of
a descriptor control block to be sent to a control unit of the
processing environment, in which the descriptor control block
includes a plurality of input/output commands to be executed, an
address of a list that informs the input/output communications
adapter where to store or fetch data received from or transmitted
to the control unit, and an address where to store ending status
from the control unit; the input/output communications adapter to
forward to the control unit the descriptor control block that
includes the plurality of input/output commands as one entity,
wherein the forwarding includes forwarding from the input/output
communications adapter to the control unit the descriptor control
block including the plurality of input/output commands in a single
communication; and the control unit to execute the plurality of
input/output commands to perform one or more input/output
operations, wherein the executing is performed absent a tracking by
the input/output communications adapter of state relative to the
individual input/output commands of the plurality of input/output
commands being executed by the control unit.
13. The system of claim 12, wherein the descriptor control block
further comprises a header providing information relating to the
input/output commands to be executed and descriptor data for one or
more of the input/output commands.
14. The system of claim 13, wherein the descriptor data comprises
control data to be provided to a device coupled to the control
unit, the device designated by a device address specified in the
header of the descriptor control block, said control data being
provided to the device absent a separate data transfer.
15. The system of claim 12, wherein a checking code is applied to
the descriptor control block to enable the control unit to check
validity of the descriptor control block.
16. The system of claim 12, wherein the list comprises one or more
modified indirect data address words, and wherein the list of one
or more modified indirect data address words comprises a single
modified indirect data address word list that describes a plurality
of data areas for a plurality of descriptor command words.
17. The system of claim 12, wherein a transfer of data resulting
from the execution of the plurality of input/output commands is
performed using a single exchange between the input/output
communications adapter and the control unit.
18. The system of claim 12, wherein the control unit provides to
the input/output communications adapter at least one of data and
status resulting from execution of the plurality of input/output
commands, wherein a transfer of data resulting from the execution
of the plurality of input/output commands is performed using three
communication sequences between the input/output communications
adapter and control unit.
19. The system of claim 18, wherein the number of sequences remains
the same, even if the number of input/output commands indicated by
the location specified in the transport control word increases.
20. The system of claim 12, wherein the input/output communications
adapter comprises a channel, and the plurality of input/output
commands comprise a plurality of channel commands specified by one
or more channel command words, wherein each channel command word
comprises a command code, one or more flags and a count field.
Description
TECHNICAL FIELD
This invention relates, in general, to input/output processing, and
in particular, to using a transport control word to reduce
input/output communications during input/output processing.
BACKGROUND OF THE INVENTION
Input/output (I/O) operations are used to transfer data between
memory and input/output devices of a processing environment.
Specifically, data is written from memory to one or more
input/output devices, and data is read from one or more
input/output devices to memory by executing input/output
operations.
To facilitate processing of input/output operations, an
input/output subsystem of the processing environment is employed.
The input/output subsystem is coupled to main memory and the
input/output devices of the processing environment and directs the
flow of information between memory and the input/output devices.
One example of an input/output subsystem is a channel subsystem.
The channel subsystem uses channel paths as communications media.
Each channel path includes a channel coupled to a control unit, the
control unit being further coupled to one or more input/output
devices.
The channel subsystem employs channel command words to transfer
data between the input/output devices and memory. A channel command
word specifies the command to be executed, and for commands
initiating certain I/O operations, it designates the memory area
associated with the operation, the action to be taken whenever
transfer to or from the area is completed, and other options.
During input/output processing, a list of channel command words is
fetched from memory by a channel. The channel parses each command
from the list of channel command words and forwards a number of the
commands, each command in it's own entity, to a control unit
coupled to the channel. The control unit then processes the
commands. The channel tracks the state of each command and controls
when the next set of commands are to be sent to the control unit
for processing. The channel ensures that each command is sent to
the control unit in it's own entity.
SUMMARY OF THE INVENTION
Enhancements to the above processing of commands are needed. For
example, a need exists for a capability that enables multiple
commands to be sent to the control unit as a single entity. A
further need exists for a capability that eliminates the need for
the channel to track the status of the individual commands being
executed by the control unit. A need exists for a capability that
reduces communication (e.g., exchanges and sequences) between the
channel and control unit during I/O processing.
The shortcomings of the prior art are overcome and additional
advantages are provided through the provision of a computer program
product for facilitating input/output processing of a processing
environment. The computer program product includes, for instance, a
storage medium readable by a processor and storing instructions for
execution by the processor for performing a method. The method
including, for instance, obtaining by an input/output
communications adapter of the processing environment a transport
control word, the transport control word including a count of the
total amount of data being transferred, an address of a descriptor
control block to be sent to a control unit of the processing
environment, in which the descriptor control block includes a
plurality of input/output commands to be executed, an address of a
list that informs the input/output communications adapter where to
store or fetch data received from or transmitted to the control
unit, and an address where to store ending status from the control
unit; forwarding from the input/output communications adapter to
the control unit the descriptor control block that includes the
plurality of input/output commands as one entity, wherein the
forwarding includes forwarding from the input/output communications
adapter to the control unit the descriptor control block including
the plurality of input/output commands in a single communication;
and executing by the control unit the plurality of input/output
commands to perform one or more input/output operations, wherein
the executing is performed absent a tracking by the input/output
communications adapter of state relative to the individual
input/output commands of the plurality of input/output commands
being executed by the control unit.
Systems and methods corresponding to the above-summarized computer
program product are also described and may be claimed herein.
Additional features and advantages are realized through the
techniques of the present invention. Other embodiments and aspects
of the invention are described in detail herein and are considered
a part of the claimed invention.
BRIEF DESCRIPTION OF THE DRAWINGS
One or more aspects of the present invention are particularly
pointed out and distinctly claimed as examples in the claims at the
conclusion of the specification. The foregoing and other objects,
features, and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
FIG. 1 depicts one embodiment of a processing environment
incorporating and using one or more aspects of the present
invention;
FIG. 2a depicts one example of a channel command word;
FIG. 2b depicts one example of a channel command word channel
program;
FIG. 3 depicts one embodiment of a link protocol used in
communicating between the channel and control unit to execute the
channel command word channel program of FIG. 2b;
FIG. 4 depicts one embodiment of a transport control word channel
program, in accordance with an aspect of the present invention;
FIG. 5 depicts one embodiment of a link protocol used to
communicate between a channel and control unit to execute the
transport control word channel program of FIG. 4, in accordance
with an aspect of the present invention;
FIG. 6 depicts one embodiment of a link protocol used to
communicate between a channel and control unit in order to execute
four read commands of a channel command word channel program;
FIG. 7 depicts one embodiment of a link protocol used to
communicate between a channel and control unit to process the four
read commands of a transport control word channel program, in
accordance with an aspect of the present invention;
FIG. 8 depicts one embodiment of a transport control word used in
accordance with an aspect of the present invention;
FIG. 9 depicts one embodiment of a channel command word descriptor
specified by the transport control word of FIG. 8 and used in
accordance with an aspect of the present invention;
FIG. 10 depicts one embodiment of ending status specified by the
transport control word of FIG. 8 and used in accordance with an
aspect of the present invention;
FIG. 11 depicts one embodiment of response information received for
a channel command word channel program;
FIG. 12 depicts one embodiment of response information received for
a transport control word channel program, in accordance with an
aspect of the present invention; and
FIG. 13 depicts one embodiment of a computer program product
incorporating one or more aspects of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
In accordance with an aspect of the present invention, input/output
processing is facilitated by reducing communications between
components of a processing environment used to perform the
input/output processing. For instance, the number of exchanges and
sequences between an input/output (I/O) communications adapter,
such as a channel, and a control unit is reduced. This is
accomplished by sending a plurality of commands from the I/O
communications adapter to the control unit as a single entity for
execution by the control unit, and by the control unit sending the
data resulting from the commands, if any, as a single entity.
The plurality of commands are included in a descriptor, referred to
herein as a channel command word descriptor, an address of which is
specified in a transport control word. The transport control word
is sent from the operating system or other application to the I/O
communications adapter, which in turn forwards the descriptor to
the control unit for processing. The control unit processes each of
the commands absent a tracking of status relative to those
individual commands by the I/O communications adapter.
One example of a processing environment incorporating and using one
or more aspects of the present invention is described with
reference to FIG. 1. Processing environment 100 includes, for
instance, a main memory 102, one or more central processing units
(CPU) 104, a storage control element 106, a channel subsystem 108,
one or more control units 110 and one or more input/output (I/O)
devices 112, each of which is described below.
Main memory 102 stores data and programs, which are input from
input devices 112. Main memory 102 is directly addressable and
provides for high-speed processing of data by central processing
units 104 and channel subsystem 108.
Central processing unit 104 is the controlling center of
environment 100. It contains the sequencing and processing
facilities for instruction execution, interruption action, timing
functions, initial program loading, and other machine-related
functions. Central processing unit 104 is coupled to storage
control element 106 via a connection 114, such as a bidirectional
or unidirectional bus.
Storage control element 106 is coupled to main memory 102 via a
connection 116, such as a bus; to central processing units 104 via
connection 114; and to channel subsystem 108 via a connection 118.
Storage control element 106 controls, for example, the queuing and
execution of requests made by CPU 104 and channel subsystem
108.
Channel subsystem 108 is coupled to storage control element 106, as
described above, and to each of the control units via a connection
120, such as a serial link. Channel subsystem 108 directs the flow
of information between input/output devices 112 and main memory
102. It relieves the central processing units of the task of
communicating directly with the input/output devices and permits
data processing to proceed concurrently with input/output
processing. The channel subsystem uses one or more channel paths
122 as the communication links in managing the flow of information
to or from input/output devices 112. As a part of the input/output
processing, channel subsystem 108 also performs the path-management
functions of testing for channel path availability, selecting an
available channel path and initiating execution of the operation
with the input/output devices.
Each channel path 122 includes a channel 124 (channels are located
within the channel subsystem, in one example, as shown in FIG. 1),
one or more control units 110 and one or more connections 120. In
another example, it is also possible to have one or more dynamic
switches as part of the channel path. A dynamic switch is coupled
to a channel and a control unit and provides the capability of
physically interconnecting any two links that are attached to the
switch.
Also located within channel subsystem 108 are subchannels (not
shown). One subchannel is provided for and dedicated to each
input/output device accessible to a program through the channel
subsystem. A subchannel (e.g., a data structure, such as a table)
provides the logical appearance of a device to the program. Each
subchannel provides information concerning the associated
input/output device 112 and its attachment to channel subsystem
108. The subchannel also provides information concerning
input/output operations and other functions involving the
associated input/output device. The subchannel is the means by
which channel subsystem 108 provides information about associated
input/output devices 112 to central processing units 104, which
obtain this information by executing input/output instructions.
Channel subsystem 108 is coupled to one or more control units 110.
Each control unit provides the logic to operate and control one or
more input/output devices and adapts, through the use of common
facilities, the characteristics of each input/output device to the
link interface provided by the channel. The common facilities
provide for the execution of input/output operations, indications
concerning the status of the input/output device and control unit,
control of the timing of data transfers over the channel path and
certain levels of input/output device control.
Each control unit 110 is attached via a connection 126 (e.g., a
bus) to one or more input/output devices 112. Input/output devices
112 receive information or store information in main memory 102
and/or other memory. Examples of input/output devices include card
readers and punches, magnetic tape units, direct access storage
devices, displays, keyboards, printers, pointing devices,
teleprocessing devices, communication controllers and sensor based
equipment, to name a few.
One or more of the above components of the processing environment
are further described in "IBM.RTM. z/Architecture Principles of
Operation," Publication No. SA22-7832-04, 5th Edition, September
2005; U.S. Pat. No. 5,461,721 entitled "System For Transferring
Data Between I/O Devices And Main Or Expanded Storage Under Dynamic
Control Of Independent Indirect Address Words (IDAWS)," Cormier et
al., issued Oct. 24, 1995; and U.S. Pat. No. 5,526,484 entitled
"Method And System For Pipelining The Processing Of Channel Command
Words," Casper et al., issued Jun. 11, 1996, each of which is
hereby incorporated herein by reference in its entirety. IBM is a
registered trademark of International Business Machines
Corporation, Armonk, N.Y., USA. Other names used herein may be
registered trademarks, trademarks or product names of International
Business Machines Corporation or other companies.
In one embodiment, to transfer data between devices 112 and memory
102, channel command words are used. A channel command word
specifies the command to be executed, and includes other fields to
control processing. One example of a channel command word is
described with reference to FIG. 2a. A channel command word 200
includes, for instance, a command code 202 specifying the command
to be executed (e.g., read, read backward, control, sense and
write); a plurality of flags 204 used to control the I/O operation;
for commands that specify the transfer of data, a count field 206
that specifies the number of bytes in the storage area designated
by the CCW to be transferred; and a data address 208 that points to
a location in main memory that includes data, when direct
addressing is employed, or to a list (e.g., contiguous list) of
modified indirect data address words (MIDAWs) to be processed, when
modified indirect data addressing is employed. Modified indirect
addressing is further described in U.S. application Ser. No.
11/464,613, entitled "Flexibly Controlling The Transfer Of Data
Between Input/Output Devices And Memory," Brice et al., filed Aug.
15, 2006, which is hereby incorporated herein by reference in its
entirety.
One or more channel command words (CCWS) arranged for sequential
execution form a channel program, referred to herein as a CCW
channel program. The CCW channel program is set up by, for
instance, the operating system, or other software. The software
sets up the CCWs and obtains the addresses of memory assigned to
the channel program. An example of a CCW channel program is
described with reference to FIG. 2b. A CCW channel program 210
includes, for instance, a define extent channel command word (CCW)
212 that has a pointer 214 to a location in memory of define extent
data 216 to be used with the define extent command. In this
example, a transfer in channel (TIC) 218 follows the define extent
command that refers the channel program to another area in memory
(e.g., an application area) that includes one or more other CCWs,
such as a locate record 217 that has a pointer 219 to locate record
data 220, and one or more read CCWs 221. Each read CCW 220 has a
pointer 222 to a data area 224. The data area includes an address
to directly access the data or a list of data address words (e.g.,
MIDAWs or IDAWs) to indirectly access the data. Further, CCW
channel program 210 includes a predetermined area in the channel
subsystem defined by the device address called the subchannel for
status 226 resulting from execution of the CCW channel program.
The processing of a CCW channel program is described with reference
to FIG. 3, as well as with reference to FIG. 2b. In particular,
FIG. 3 shows an example of the various exchanges and sequences that
occur between a channel and a control unit when a CCW channel
program is executing. The link protocol used for the communications
is FICON (Fibre Connectivity), in this example. Information
regarding FICON is described in "Fibre Channel Single Byte Command
Code Sets-2 Mapping Protocol (FC-SB-3), T11/Project 1357-D/Rev.
1.6, INCITS (March 2003), which is hereby incorporated herein by
reference in its entirety.
Referring to FIG. 3, a channel 300 opens an exchange with a control
unit 302 and sends a define extent command and data associated
therewith 304 to control unit 302. The command is fetched from
define extent CCW 212 (FIG. 2b) and the data is obtained from
define extent data area 216. The channel uses TIC 218 to locate the
locate record CCW and the read CCW. It fetches the locate record
command 305 (FIG. 3) from the locate record CCW 217 (FIG. 2B) and
obtains the data from locate record data 220. The read command 306
(FIG. 3) is fetched from read CCW 221 (FIG. 2B). Each is sent to
the control unit.
The control unit opens an exchange 308 with the channel, in
response to the open exchange of the channel. This can occur before
or after locate command 305 and/or read command 306. Along with the
open exchange, a response (CMR) is forwarded to the channel. The
CMR provides an indication to the channel that the control unit is
active and operating.
The control unit sends the requested data 310 to the channel.
Additionally, the control unit provides the status to the channel
and closes the exchange 312. In response thereto, the channel
stores the data, examines the status and closes the exchange 314,
which indicates to the control unit that the status has been
received.
The processing of the above CCW channel program to read 4k of data
requires two exchanges to be opened and closed and seven sequences.
In accordance with an aspect of the present invention, the number
of exchanges and sequences between the channel and control unit is
reduced by collapsing multiple commands of the channel program into
one command word, referred to as a transport control word (TCW).
Specifically, the transport control word points to a channel
command word descriptor (CCWD) that includes the multiple commands.
The TCW is executed by the host channel and is not sent or seen by
the control unit.
One example of a channel program to read 4k of data, as in FIG. 2b,
but includes a transport control word, instead of separate
individual channel command words, is described with reference to
FIG. 4. As shown, a channel program 400, referred to herein as a
TCW channel program, includes a transport control word 402
specifying a location in memory of a channel command word
descriptor (CCWD) 404, as well as a location in memory of a data
area 406 or a MIDAL 410 (i.e., a list of MIDAWs) that points to
data area 406, and a status area 408. Transport control words,
channel command word descriptors and status are described in
further detail below.
The processing of a TCW channel program is described with reference
to FIG. 5. The link protocol used for these communications is, for
instance, the fibre channel protocol (FCP). In particular, the
three phases of the FCP link protocol are used, allowing host bus
adapters to be used that support FCP to support data transfers
controlled by CCWs. FCP and its phases are described further in
"Information Technology--Fibre Channel Protocol for SCSI, Third
Version (FCP-3)," T10 Project 1560-D, Revision 4, Sep. 13, 2005,
which is hereby incorporated herein by reference in its
entirety.
Referring to FIG. 5, a channel 500 opens an exchange with a control
unit 502 and sends the channel command word descriptor 504 to the
control unit. In one example the CCWD and sequence initiative are
transferred to the control unit in a FCP command, referred to as
FCP_CMND IU. The control unit executes the multiple commands of the
channel command word descriptor (e.g., define extent command,
locate record command, read command) and forwards the data 506 to
the channel via, for instance, a FCP_Data IU. It also provides
status and closes the exchange 508. As one example, final status is
sent in a FCP status frame that has a bit active in, for instance,
byte 10 or 11 of the FCP_RSP IU Payload. The FCP_RES_IU Payload is
used to transport FICON ending status along with the control unit
queue time, disconnect time, active time, the offset of the last
DCW executed, the residual data byte count of the last DCW
executed, the residual data byte count of the CCWD, and possible
sense data.
In a further example, to write 4k of customer data, the channel
uses the FCP link protocol phases, as follows: 1. Transfer the CCWD
in the FCP_CMND IU. 2. Transfer the IU of data, and sequence
initiative to the control unit. (FCP Transfer Ready Disabled) 3
Final status is sent in a FCP status frame that has a bit active
in, for instance, byte 10 or 11 of the FCP_RSP IU Payload. The
FCP_RES_INFO field or sense field is used to transport FICON ending
status along with the control unit queue time, disconnect time,
active time, the offset of the last DCW executed, the residual data
byte count of the last DCW executed, the residual data byte count
of the CCWD, and possible sense data.
By executing the TCW channel program of FIG. 4, there is only one
exchange opened and closed (see also FIG. 5), instead of two
exchanges for the CCW channel program of FIG. 2b (see also FIG. 3).
Further, for the TCW channel program, there are three communication
sequences (see FIGS. 4-5), as compared to seven sequences for the
CCW channel program (see FIGS. 2b-3).
The number of exchanges and sequences remain the same for a TCW
channel program, even if additional commands are added to the
program. Compare, for example, the communications of the CCW
channel program of FIG. 6 with the communications of the TCW
channel program of FIG. 7. In the CCW channel program of FIG. 6,
each of the commands (e.g., define extent command 600, locate
record command 601, read command 602, read command 604, read
command 606, locate record command 607 and read command 608) are
sent in separate sequences from the channel 610 to the control unit
612. Further, each 4 k block of data (e.g., data 614-620) is sent
in separate sequences from control unit 612 to channel 610. This
CCW channel program requires two exchanges to be opened and closed
(e.g., open exchanges 622, 624 and close exchanges 626, 628), and
fourteen communications sequences. This is compared to the three
sequences and one exchange for the TCW channel program of FIG. 7,
which accomplishes the same task as the CCW channel program of FIG.
6.
As depicted in FIG. 7, a channel 700 opens an exchange with a
control unit 702 and sends a channel command word descriptor 704 to
the control unit. The CCWD includes the define extent command, the
two locate record commands, and the four read commands, as
described above. In response to receiving the CCWD, the control
unit executes the commands and sends, in a single sequence, the 16
k of data 706 to the channel. Additionally, the control unit
provides status to the channel and closes the exchange 708. Thus,
the TCW channel program requires much less communications to
transfer the same amount of data as the CCW channel program.
Further details regarding the transport control word, the channel
command word descriptor and status are described with reference to
FIGS. 8-10. In particular, one embodiment of a transport control
word is described with reference to FIG. 8, one embodiment of a
channel command word descriptor referred to by the transport
control word is described with reference to FIG. 9, and one
embodiment of ending status also referred to by the transport
control word is described with reference to FIG. 10.
Referring to FIG. 8, in one example, a transport control word 800
includes a plurality of fields, such as, for instance: a) Command
Field 802: The command field indicates if the command is a TCW
channel command or a legacy channel CCW. A TCW channel command is
an X8 command with X not equal to zero. As examples, the X8 command
field includes one of the following commands: 1) For x=one, as one
example, the command is a write TCW command that transfers a
channel command word descriptor to the control unit, as well as
customer data, per the channel command word descriptor data byte
count field in the transport control word; and 2) For x=two, as one
example, the command is a read TCW command that transfers a channel
command word descriptor to the control unit, and the channel
command word descriptor data byte count is the total amount of data
the control unit will transfer to the channel; b) Flags 804: The
flag field may include one or more flags. In this example, it
includes a MIDAW flag that indicates whether modified indirect
addressing or direct addressing is being used. If the flag is
active, an address 810 in the transport control word is the address
of a first modified indirect data address word (MIDAW) of a
modified indirect data address list (MIDAL). Otherwise, the address
is a data address used for direct addressing; c) CCWD Length 806:
This field includes the length of the channel command word
descriptor specified by this transport control word; d) CCWD Data
Byte Count 808: This field includes the total amount of customer
data to be transferred by all of the descriptor command words
(DCWs), described below, in the channel command word descriptor; e)
Address of MIDAW or Data Address 810: This field provides the
address of a MIDAW, assuming flag field 804 indicates it should be
a MIDAW address, or an address of customer data; f) Address of the
CCWD 812: This field includes an address to locate in memory the
channel command word descriptor. The channel command word
descriptor is further described below. g) Address of Status 814:
This field includes an address to locate in memory an ending
completion status for this transport control word. Further
information regarding the ending status is described below.
The three addresses defined by the transport control word
including, MIDAW or data address 810, CCWD address 812, and status
address 814, are used by, for instance, a host bus adapter to
execute the equivalent of a FCP operation. This enables the FCP
link phases, instead of FICON phases, to be used in communications,
thereby significantly increasing performance and efficiency of the
channel subsystem.
As indicated above, the transport control word specifies a channel
command word descriptor to be used. The channel command word
descriptor includes the multiple commands to be executed by the
control unit. The commands are executed independent of the channel
in that status relative to execution of the individual commands is
not tracked by the channel. The control unit receives the multiple
commands as a single unit and has the responsibility of executing
the commands, in an appropriate manner. In one example, the CCWD is
sent to the control unit as the FCP_CMND IU payload in the FCP link
protocol. By relieving the channel of the responsibility of
tracking individual commands, performance of the channel is
significantly enhanced. Moreover, the control unit benefits by
seeing the entire channel program at one time.
One embodiment of a channel command word descriptor (CCWD) is
described with reference to FIG. 9. A channel command word
descriptor 900 has three main parts, including, for instance, a
header 902, multiple DCWs 904 and descriptor data 906, each of
which is described below.
CCWD header 902 includes the following fields, as one example: a)
Channel Image Id 910: This field identifies the channel involved in
the communication; b) Control Unit Image Id 912: This field
identifies the control unit communicating with the channel
identified by channel image id 910; c) Device Address 914: This
field identifies the device coupled to the control unit that is
involved in the I/O communications; d) Read or Write field 916:
This field indicates whether the I/O operations are read or write;
e) CDB CMD 918: This field is used to identify this as a CCWD; f)
I/O Priority 920: This field indicates the priority of this I/O; g)
CCWD Length 922: This field indicates the length of the CCWD; h) #
DCWs 924: This field indicates the number of descriptor command
words for this CCWD; and i) CCWD Data Byte Count 926: This field
describes the total customer data to be transferred by the
CCWD.
Each descriptor command word 904 includes a plurality of fields,
such as, for instance: a) Command Field 930: This field includes
the CCW command (e.g., control commands like define extent and
locate record; read; write; etc.); b) Flag Field 932: This field
may include one or more flags. In this example, flag field 932
includes a command chain flag indicating whether command chaining
is present; and a descriptor data present flag indicating whether
descriptor data is present in the CCWD following this DCW. This
flag is active for write control, when the write control command
requires descriptor data; c) Byte Count Field 934: If this is a
control command, the count is the number of bytes of control data
in the CCWD; otherwise, it is the count of customer data to be
transferred by this DCW. If the DCW command is a command
intermediate or a no op command, the byte count field is zero.
Descriptor data 906 includes the data 936 for a DCW write control
command. This data is in the CCWD following the DCW the data is for
and its presence is made known by the flag field in the DCW. By
specifying control data directly in the descriptor list, the device
can obtain the data without requiring the device to perform a
separate data transfer to obtain it.
In one embodiment, a checking code, such as a cyclic redundancy
check (e.g., FICON CRC), a longitudinal redundancy check (LRC), a
checksum, etc., is applied across the CCWD data transferred per the
sum of the DCW byte counts in the CCWD, and a separate checking
code is applied to the CCWD, when it is transmitted to the control
unit. For example, a checking code is applied to the total data
being transferred by the CCWD. This is at a higher level than the
CRC applied at the transport level. The check is applied to each
data packet sent, and then accumulated and verified at the receiver
end to ensure the entire data, as specified by the CCWD data byte
count, arrived completely and without errors.
As a further example, for the CCWD itself, a checking code is
applied. For instance, the code is appended to the information. The
control unit receives the information, checks the code, and if
valid, the information is considered valid.
The transport control word also specifies a location for ending
status. This allows the operating system to specify an area in
storage for the extra timers and count information from the control
unit for a TCW operation and for sense data, thus, guaranteeing the
delivery of concurrent sense data on every unit check condition.
One example of ending status is described with reference to FIG.
10.
In one embodiment, an ending status control block 1000 includes the
following fields: a) DCW Residual Byte Count 1002: This field
indicates the residual byte count of a failed DCW (i.e., where
execution of the DCWs was interrupted); b) Sense Length 1004: This
field specifies the length of sense data appended at the end of
this control block in appended sense data; c) Response Length 1006:
This field indicates the length of the response portion of this
control block; d) CH Image Id 1008: This field identifies the
channel involved in the communication; e) CU Image Id 1010: This
field identifies the control unit communicating with the channel
identified by channel image id 1008; f) Device Address 1012: This
field identifies the device coupled to the control unit that is
involved in the I/O communications; g) Status Flags 1014: This
field specifies one or more status flags. Examples of status flags
are described in "Fibre Channel Single Byte Command Code Sets-2
Mapping Protocol (FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS
(March 2003), which is hereby incorporated herein by reference in
its entirety; h) Status 1016: This field identifies status of the
communication, including, for instance, device status, which is
further described in "IBM.RTM. z/Architecture Principles of
Operation," Publication No. SA22-7832-04, 5th Edition, September
2005, hereby incorporated herein by reference in its entirety; i)
CCWD Residual Byte Count 1020: This field indicates the residual
byte count of the CCWD Data Byte Count, which is the remaining
count of data that was not transferred for the whole CCWD; j) DCW
Offset 1022: If all DCWs are not executed in the CCWD, this is the
DCW offset in the CCWD of the failed DCW; k) Queue Time Parameter
1024: This field specifies the amount of time the control unit had
the I/O operation on it's queue with the exchange open to the
channel; l) Defer Time Parameter 1026: This field specifies the
amount of time the control unit waited for the data, with the
exchange open to the channel, because of a control unit data cache
miss. The control unit had to access the media to reference the
requested data; m) Control Unit Active Time 1028: This field
specifies the time the control unit is active executing a TCW; n)
Appended Sense Data, if any 1030: This field includes sense for the
case the control unit encountered a unit check during the I/O
operation.
Status is further described in "IBM.RTM. z/Architecture Principles
of Operation," Publication No. SA22-7832-04, 5th Edition, September
2005; and queue time, defer time and appended sense are further
described in "Fibre Channel Single Byte Command Code Sets-2 Mapping
Protocol (FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March
2003), each of which is hereby incorporated herein by reference in
its entirety.
For legacy FICON, the command response is an important measurement
point in the operation of a CCW channel program. FIG. 11 is a
timeline as seen by the channel that depicts various timing points
kept track of by the channel subsystem for a CCW channel program.
As an example, the channel sees Start subchannel A 1100, CMR B
1102, Disconnect C 1104, Reconnect D 1106 and Ending Status E 1108.
The control unit provides the channel with the CU queue time and CU
defer time at ending status time.
The legacy channel subsystem, in effect, performs a number of steps
to gather various times for channel subsystem measurements. For
example, with reference to FIG. 11, it timestamps the time of start
Subchannel at A 1100, and it timestamps the time of CMR at B 1102.
At disconnect time C 1104, it calculates connect time (CT=C-B). It
timestamps the time of reconnect at D 1106, and timestamps Ending
Status time at E 1108. From there, it calculates total connect time
CT=(C-B)+(E-D); total start pending time SP=(B-A); and disconnect
time DT=(E-A)-CT-SP).
For a TCW, however, the channel does not get a Command Response CMR
to know when the control unit started the I/O operation. For
instance, with reference to the timeline of FIG. 12, it only sees
the Start Subchannel A 1200 and the Ending status E 1202. The
channel does not see for a TCW operation the CMR B 1204 time, and
the time required to retrieve data from the media starting at C
1206 and ending at D 1208. The time to retrieve data from the media
is part of the CU defer time for a TCW. The CU queue time (not
shown) and CU defer time are provided by the control unit at ending
status time.
Thus, for a TCW channel program, the channel timestamps the time of
Start Subchannel at A 1200 and the ending status time at E 1202,
but it is the control unit that performs the tracking of when the
operation started and the total time to execute the individual
commands and provide this measurement data as part of the ending
status.
As one example, the control unit reports the following at ending
status: AT=Active time=(C-B)+(E-D) in FIG. 12--this is CU active
time 1028 in FIG. 10; QT=CU queue time--this is the amount of time
the control unit had the operation on it's queue before starting
the operation and is the queue time parameter 1024 in FIG. 10; and
DT=Defer time=(D-C) in FIG. 12--this is defer time parameter 1026
in FIG. 10.
From the timers provided by the control unit and the beginning and
ending timestamps provided by the channel subsystem at A and E on
FIG. 12, the same measurement data is provided for a TCW command as
for the legacy CCW commands. The I/O subsystem determines: CMR time
(B-A (FIG. 12))=(E-A)-AT-DT-QT; Total connect time CT=CU reported
active time AT (1028 in FIG. 10); Total start pending time
SP=(E-A)-AT-DT; and Disconnect time=CU reported defer time=(D-C)
(1026 in FIG. 10).
Therefore, the control unit has the responsibility of tracking
state information of the individual commands and providing
measurement data relating thereto, relieving the channel of this
responsibility. The operating system communicates directly with the
control unit using the channel only as a conduit. The channel does
not track the state information of the individual commands but the
I/O subsystem provides the same measurement data as with legacy
CCWs by using the I/O subsystem timestamps A and E and the three
timers from the control unit, and thus, the same measurement data
is provided to the operating system. At the same time, the workload
of the channel is reduced.
One or more aspects of the present invention can be included in an
article of manufacture (e.g., one or more computer program
products) having, for instance, computer useable media. The media
has therein, for instance, computer readable program code means or
logic (e.g., instructions, code, commands, etc.) to provide and
facilitate the capabilities of the present invention. The article
of manufacture can be included as a part of a computer system or
sold separately.
One example of an article of manufacture or a computer program
product incorporating one or more aspects of the present invention
is described with reference to FIG. 13. A computer program product
1300 includes, for instance, one or more computer usable media 1302
to store computer readable program code means or logic 1304 thereon
to provide and facilitate one or more aspects of the present
invention. The medium can be an electronic, magnetic, optical,
electromagnetic, infrared, or semiconductor system (or apparatus or
device) or a propagation medium. Examples of a computer readable
medium include a semiconductor or solid state memory, magnetic
tape, a removable computer diskette, a random access memory (RAM),
a read-only memory (ROM), a rigid magnetic disk and an optical
disk. Examples of optical disks include compact disk-read only
memory (CD-ROM), compact disk-read/write (CD-R/W) and DVD.
A sequence of program instructions or a logical assembly of one or
more interrelated modules defined by one or more computer readable
program code means or logic direct the performance of one or more
aspects of the present invention.
Advantageously, in accordance with one or more aspects of the
present invention, I/O processing is enhanced by enabling the
operating system to communicate directly with the control units and
by relieving the I/O communications adapters of having to track all
the state information regarding individual commands being
processed. That is, a direct communication path is established
between an operating system and a control unit, such that the
operating system can deliver a list of command words to the device
through the channel subsystem without the channel subsystem
requiring any visibility to or processing of the individual
commands. This reduces the work of the communications adapter, and
enhances the performance thereof. Further, the control unit is
benefited by having an understanding of all the commands to be
performed by the control unit for a channel program. Additionally,
more precise measurement data is provided by having the control
unit provide the various times for intervals it controls directly,
rather than having the channel subsystem infer the times from
imprecise signals on the interface.
In accordance with one or more aspects of the present invention,
well behaved (e.g., predictable execution known by the operating
system or software at build time) CCW chains are collapsed into one
control block referred to herein as the CCW Descriptor (CCWD) and
is referenced by a CCW referred to herein as the transport control
word. Command chain CCWs, as well as data chain CCWs, may be
collapsed into one CCWD. This reduces the number of sequences and
exchanges required to transfer a given amount of data. Instead of
requiring separate sequences for individual device commands, a
single exchange is used. As one example, this results in a 2.times.
reduction over FICON in both exchanges and sequences required to
transfer 4k of data. This enables FICON to be competitive with FCP
particularly on small block transfers. Instead of using the FICON
link phases, FCP link phases are used. However, the information
that is in the FCP_CMND IU and FCP_RSP IU is not FCP, except for
bits and bytes that have to be sent in the FCP_CMND IU to allow a
FCP host bus adapter to work with the protocol.
The TCW provides the information for an I/O communications adapter
to transport the list of CCW commands to the control unit, as well
as transfers customer data to or from the control unit.
Advantageously, a channel subsystem using one or more aspects of
the present invention can also continue to use CCW channel
programs, as well as the TCW channel programs. By using TCWs, the
performance of an I/O operation that transfers, for instance, small
blocks of data is improved. Moreover, the use of TCWs and CCWDs
enables a place for sense data, which may be sent with the ending
status.
Although various embodiments are described above, these are only
examples. Processing environments other than those described
herein, including others that use I/O subsystems, other than
channel subsystems, can incorporate and use one or more aspects of
the present invention. Further, although various control blocks
have been shown, the location of the information within those
control blocks may be other than shown herein. Further, each
control block may include additional, less or different information
than described herein. For instance, there may be additional, fewer
and/or different fields, including fields that may include
additional, fewer and/or different flags. Further, there may be
additional, fewer and/or different field sizes. Yet further,
although main memory is mentioned or described in various portions
of the embodiment, one or more aspects of the present invention may
be applicable to other memory. Still further, although
communications protocols, such as FICON and FCP, are described
herein, one or more aspects of the present invention are applicable
to other protocols.
Moreover, an environment may include an emulator (e.g., software or
other emulation mechanisms), in which a particular architecture or
subset thereof is emulated. In such an environment, one or more
emulation functions of the emulator can implement one or more
aspects of the present invention, even though a computer executing
the emulator may have a different architecture than the
capabilities being emulated. As one example, in emulation mode, the
specific instruction or operation being emulated is decoded, and an
appropriate emulation function is built to implement the individual
instruction or operation.
In yet other examples, TCW channel programs performing other
commands may include one or more aspects of the present invention.
Further, TCW channel programs can read other amounts of data than
described herein and still benefit from one or more aspects of the
present invention. Numerous other examples and modifications are
possible without departing from the spirit of the present
invention.
In an emulation environment, a host computer includes, for
instance, a memory to store instructions and data; an instruction
fetch unit to fetch instructions from memory and to optionally,
provide local buffering for the fetched instruction; an instruction
decode unit to receive the instruction fetch unit and to determine
the type of instructions that have been fetched; and an instruction
execution unit to execute the instructions. Execution may include
loading data into a register for memory; storing data back to
memory from a register; or performing some type of arithmetic or
logical operation, as determined by the decode unit. In one
example, each unit is implemented in software. For instance, the
operations being performed by the units are implemented as one or
more subroutines within emulator software.
Further, a data processing system suitable for storing and/or
executing program code is usable that includes at least one
processor coupled directly or indirectly to memory elements through
a system bus. The memory elements include, for instance, local
memory employed during actual execution of the program code, bulk
storage, and cache memory which provide temporary storage of at
least some program code in order to reduce the number of times code
must be retrieved from bulk storage during execution.
Input/Output or I/O devices (including, but not limited to,
keyboards, displays, pointing devices, etc.) can be coupled to the
system either directly or through intervening I/O controllers.
Network adapters may also be coupled to the system to enable the
data processing system to become coupled to other data processing
systems or remote printers or storage devices through intervening
private or public networks. Modems, cable modems, and Ethernet
cards are just a few of the available types of network
adapters.
The capabilities of one or more aspects of the present invention
can be implemented in software, firmware, hardware, or some
combination thereof. At least one program storage device readable
by a machine embodying at least one program of instructions
executable by the machine to perform the capabilities of the
present invention can be provided.
The flow diagrams depicted herein are just examples. There may be
many variations to these diagrams or the steps (or operations)
described therein without departing from the spirit of the
invention. For instance, the steps may be performed in a differing
order, or steps may be added, deleted, or modified. All of these
variations are considered a part of the claimed invention.
Although preferred embodiments have been depicted and described in
detail there, it will be apparent to those skilled in the relevant
art that various modifications, additions, substitutions and the
like can be made without departing from the spirit of the invention
and these are therefore considered to be within the scope of the
invention as defined in the following claims.
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